The face of the

It is of great

tooth through the centre of the spindle-hole in the centre of the saw. saw-tooth should be at an angle of from 20° to 30° to that line (Fig. 280). importance that the points of the teeth are absolutely the same length from the centre of the saw. To ensure this, the points of the teeth are frequently "stripped." This is done by holding a piece of hard sandstone against the points of the teeth, keeping the saw revolving at about half-speed during the operation. The teeth should then be sharpened up to the face-point-i.e., all trace of stripping should be removed from each tooth, but nothing more. The blades of saws should at all times be kept at a uniform tension throughout. The uniformity of tension is sometimes destroyed in the centre by continual or frequent heating of the saw-spindle, thus causing the saw to go into the form of a shallow cup. In the outer rim the tension is disturbed by insufficient "set," by being frequently jammed by the vice-action of dried or twisted logs, by bad trimming, and by having the guides too tight, all of which tend to expand the outer edge of the saw, twisting it, and thereby causing it to cut up the logs in an erratic manner.

The cost of saws varies with the thickness, diameter, and quality of the plate. They are usually sold at so much per inch, measuring across their diameter to the points of the teeth. The catalogue prices seldom alter, but the discounts, which often exceed 50 per cent of the catalogue price, vary with every change in the cost of raw material and labour. A 42-inch circular saw, gauge 10, costs from 72s. to 75s., while it is catalogued at 180s. A 36-inch saw, gauge 11, costs 44s., while it is catalogued at 120s. Thinner saws are cheaper in proportion.

The usual thickness of saws in use in saw-mills worked by landed proprietors is between 10 and 12 B.W.G., even when of small diameter. This is because they are more rigid, and do not reflect bad trimming so readily. The proper thickness should be from 13 to 16 B.W.G. Let me give an example to illustrate what the difference would be. Two men are required to cut, say, 4000 superficial feet of 1-inch Larch boarding. The one works gauge No. 16, and the other gauge 12. To produce 4000 superficial feet with the No. 16 saw 366 ft. of rough timber is required, while the man working the No. 12 requires a little over 20 ft. more-viz., 386 cub. ft.-being a loss of timber alone of about 6 per cent, or 20s. 6d. ; then cartage of extra timber at 1d. per cubic foot, 1s. 8d.; crosscutting at d., say, 10d.; three hours more of man and machinery at 2s., equal 6s.-in all, say, a difference of 29s. on that small quantity of wood. In other words, a very handsome profit is converted into sawdust. Any one can make the calculation for himself, and he will find that the above figures are practically correct. It is to be regretted that this is so much overlooked by those in charge of estates where timber is manufactured for estate purposes.

The size of the mill and the most convenient arrangement of the machinery are matters directly affecting economical working. For the larger class of estate mills converting annually from 50,000 to 100,000 cub. ft. of timber into sleepers, pitwood, &c., under a special foreman in charge of up to about 10 men, two saws may be driven by one good portable or traction-engine standing in the middle of the shed, the one saw being used for slabbing and the other for sawing, on two home-made wooden benches up to about 40 ft. long running along each side of part of the shed. Beyond the engine, and driven by its spare fly-wheel, a cross-cut saw may be worked by the same shafting, on benches about 16 ft. long facing each other on either side of the shed, which are used for cutting pitwood, staves, and beadingthe cross-cutting, slabbing, and sawing of the small-sized wood being carried on at the same time as the conversion of the large timber on the long benches. Sleepers of ordinary size (9 ft. x 10 in. x 5 in. =3} cub. ft.) can be turned out in such a mill at a total cost of about 11d. per sleeper.

It is only in large mills with strong driving-power that additional machinery can be added in the form of a band-saw, mortising machine, lathe, planing machine, general wood-worker or estate-carpenter, wood-wool machinery for working up waste pieces, timber-lifters, &c.

Where the estate work only consists in cutting up timber into gate-posts, fence20

VOL. II.

rails, &c., travelling engines and saw-benches may in some districts be hired at about 30s. a day, exclusive of fuel, water, and labour other than that of the sawyer and driver in charge.

The Cost of Conversion must of course vary considerably according to circumstances, as it depends on the combination of such various factors as the cost of timber-haulage, quantity, size, and quality of timber, price and quality of labour, capacity and quality of machinery, &c. Except the mill-manager, who should receive a regular salary plus a bonus on the net profit of working, all the millhands should be on piecework at so much per sleeper or per 1000 superficial feet for each different width and thickness of boards, planks, &c., the contract rate being fixed according to the known size and quality of the timber and the easily ascertained capacity of the machinery, so as to provide a good pay for a good day's work.1

There can, therefore, be no absolute rule laid down to guide one; but the following are some of the usual contract prices. If we assume that the saw-mill is situated at an average distance, not more than 1 mile, from the timber to be manufactured, the cost of carting should be d. per cubic foot, including bark. For felling and cross-cutting into lengths, no length to be under 6 ft., Scots Fir and Larch d., Spruce d. to 1d. per cubic foot; for hardwoods, 1d. to 2d. per cubic foot. The cost of sawing and stacking to season (exclusive of motive-power), from 14d. to 14d. per cubic foot-say, 4s. per 1000 superficial feet of -inch thick, to 7s. 6d. per 1000 superficial feet of 1-inch boarding (Mackenzie, op. cit., p. 144).

In his article, which should be studied by all those engaged, or about to be engaged, in converting timber for estate purposes, Mr. Mackenzie gives a list of the contract prices he pays for different kinds of standard sizes of felloes, spokes, naves, shafts, sides, bottoming, &c., for cartwright, van, lorry, coach, barrow and waggon wood, and also for timber for general purposes, such as wedges, railway keys and waggon sprags, railway-sleepers, pitsleepers and pillar wood, fencing-wood, mill rollers, barrel staves and ends, &c. Hardwood scantlings and planks of different thickness are paid at 2d. per cubic foot, and railway keys at 7s. 6d. per 1000; Scots Pine boarding per 1000 superficial feet of in. 4s. 6d., in. 5s. 6d., § in. 6s. 6d., and 1 in. 7s. 6d. ; Scots Pine and Spruce pit-sleepers (31 or 3 ft. x 5 in. x 2 in.) 2s. per 100; Larch and Pine railway-sleepers from 5s. 6d. per 100 (for 7 ft. x 7 in. x 3 in.) up to 8s. 4d. to 10s. (for 9 ft. x 9 in. × 41, or 9 ft. x 10 in. x 5 in. with 5 in. square slab on back); Larch stobs up to 4s. 8d. per 100 (for 6 ft. × 6 in. × 3 in.), and rails 7s. 6d. per 1000 lineal feet (3 in. x 1 or 1 in.); Sycamore spinning-mill rollers 3s. 6d. per gross (7 to 9 in. x 12 in.); hardwood shuttle-blocks 1s. 9d. per 100 (22 in. x 24 in. × 24 in.).

Besides the ordinary standard sizes of wood in general use which are most likely to find a ready sale from an estate mill, there are, as Mr. Mackenzie remarks (op. cit., p. 147), other uses to which the various classes of timber can be put:-"For example, the smaller sizes of Beech and Oak are sent direct from the woods to the chemical works to be made into vinegar and charcoal. Small Ash is used for tool-handles if clean grown. Bent timber of Oak or Elm is used in boat-building and boat repairs. The smaller sizes of clean Oak are cut up for telegraph-arms. Beech is used for butchers' tables, wheel-cogs, and plumbers' tools; while large well-grown Willow and Poplar are used for saddlers' and shoemakers' cutting benches, as also for railway carriage-brake blocks. Plane or Sycamore trees under 6 in. diameter, whether branches or stems, are used by turners for making fancy boxes of small sizes; those from 6 to 10 in. diameter are cut into spinning-mill pressing-rollers 7 to 9 in. long, and 1 in. thick; from 10 to 19 in. in diameter are used by cabinetmakers-to order-and for bakers' troughs and tables, rollers for washing, wringing, and mangling machines. All large cleanly grown cuts are sent direct to the calico-works for printing-blocks, but nothing less than 20 in. diameter is of use. The inferior cuts, both of the main stem and branches, are cut into barrel staves and ends. . . .

1 Handsawing costs per 100 super. ft., for boards, from 2s. 6d. -3s. (softwoods) to 3s. 6d.4s. 6d. (hardwoods); and for planks, 3s. 6d. -5s. (softwoods) to 5s.-7s. (hardwoods).

"The fact is, that in a properly managed establishment there is very little waste, and if a distilling apparatus and wood-pulper be added there need be none at all, not even of the sawdust. It is found that the charring of the latter in a common gas-retort renders it a most excellent disinfectant for stables, byres, piggeries, and poultry-houses, and after becoming saturated with the manurial ingredients, it forms, as might be expected, a very good manure."

Where log-ends have on any large scale to be broken up into firewood, this can be very quickly done by placing the flat section on a framework consisting of 2, 3, or 4 axe-edged blades set diametrically to cut into 4, 6, or 8 billets, and cleaving it with the blow of a heavy mallet, when the split pieces fall down below. Kickstamp machinery has been invented for this purpose, and consists offa heavy iron hammer raised by a hand-lever and allowed to fall on the log-section to be split.

II. The Preparation of Wood-pulp and Cellulose.-Next to the conversion of timber in saw-mills, the consumption of wood in making pulp and cellulose for paper-mills and many other industries ranks next in importance. Until about fifty years ago (see vol. i. p. 84) paper was made almost entirely from rags, but during the last thirty years especially the use of wood as a raw material for paper-making, and for many other miscellaneous purposes, has created vast new industries throughout all the woodland parts of Europe and North America.1

When the woody-fibrous substance is prepared purely by mechanical means the product is called Wood-pulp, and when the cell-substance of the pulp is also extracted chemically, the product is Cellulose. The present value in Britain of the former is about £4, 10s. a ton, and of the latter £7 a ton.

Owing to the insufficiency of our woodlands there are but few wood-pulp or cellulose factories in Britain. The latter have mainly to use imported wood as their raw material, while the preparation of the coarser wood-pulp is too heavily handicapped to compete with that ground in Scandinavia and Canada by water-power in forests where the wood is obtainable close at hand.

British imports of wood-pulp (see vol. i. p. 94) now amount annually to close on 600,000 tons, valued at about £2,500,000, which is just about one-tenth of the value of our annual wood imports. The great disadvantage under which British pulp-mills work may be judged of by the fact that at the Kellner-Partington Pulp Company's mills at Glossop, in Derbyshire, where a special acid process patented by Mr. Partington is in use with Poplar and Spruce chiefly, imported from Norway and the Baltic, the wood (poles 6 in. in diameter and cut to 6 ft. lengths) costs about 60s. per cubic fathom at the nearest seaport, and 90s. by the time it reaches the mill; and the average yield per cubic fathom is 1 ton of dry cellulose, 1 ton of water, and 1 ton of extractive, for which there is as yet no profitable use (Anderson, in Jour. Roy. Agric. Socy., 1903).-As a cubic fathom of such wood will contain about 3 tons, or 150 cub. ft., of solid contents (216 × 0·7=151·2), this means that the wood to be pulped costs about 7d. a cubic foot delivered at the mill.

For a cellulose mill to be worked at a profit it is calculated that about 80 cubic fathoms (240 tons=12,000 cub. ft.) of wood are needed weekly, or over 4000 fathoms (12,000 tons=600,000 cub. ft.) per annum, which is equivalent to the yield from

1 That paper could be made from wood has been known for at least 150 years. In the forestry museum of Munich University there is an interesting specimen of coarse dirty-brown paper made about 1750 by a country clergyman, who took his idea from the paper-like composition of a wasp's nest.

about 120 to 150 acres of 40-year-old Spruce (according to quality of soil and crop), and would therefore need from 4800 to 6000 acres of regular and well-managed Spruce-woods to provide a continuous supply of pulp-wood. The preparation of wood-pulp mechanically, however, can be carried on profitably on a very much smaller scale, and thinnings can thus be utilised, though even then there are comparatively few places in the United Kingdom where Spruce and other suitable softwoods are obtainable in sufficient quantity to keep a wood-pulp mill at work.

The out-turn from wood-pulp and cellulose factories has increased enormously throughout Northern and Central Europe during the last thirty years. In 1900 there were in Germany above 601 wood-pulp mills, of which 300 were in Saxony, which annually ground down about 35,000,000 cub. ft., or 700,000 tons, of wood, yielding about 200,000 tons weight of pulp; and there were 71 cellulose factories using about 29,750,000 cub. ft., or 595,000 tons, of wood, and producing about 170,000 tons of dry cellulose. In the mountain districts of Central and Southern Germany, where water-power is abundant, there is a very large number of small pulp-mills which grind up the wood in a simple manner; and it then pays to work on a very small scale. But the work is often done under conditions so primitive, that they would in Britain be an infringement of the Factories Act.

When the supply of rags began to be found insufficient to provide for the increased demand for paper, wood-pulp was first of all prepared mechanically and mixed with rags. But owing to the shortness of its fibre, its stiffness, and the difficulty of bleaching it and rendering it felty, it was in some respects an unsatisfactory addition, and only a makeshift as a substitute. Subsequently, however, by steaming the wood a longer-fibred substance was obtained, which could be made (without any admixture of rags) into the lower grades of paper, such as is used for newspapers, bills and posters, packing-paper, &c. The second and greater discovery was the use of chemicals to free the pulp from incrusting substances and enable the cellulose to be obtained in nearly a pure condition. This refined product proved so good a substitute for rags, that it has almost entirely taken their place in the manufacture of paper.

Pure Cellulose (CHO), not yet found in any plant, is white, silky, translucent, hygroscopic, and without taste or smell (see p. 427); and when prepared, it retains the form of the portion of the tree from which it has been obtained. From thoroughly lignified tissues, like the heartwood of Oak, Elm, and Larch, cellulose can either only be partially obtained, or else not at all. It is not completely soluble in any solvent yet discovered. In ammoniated oxide of copper it swells so rapidly that it seems to dissolve; but on acids or salts, or even a considerable quantity of water being added, it is deposited as a structureless, cloudy, or thread-like mass. Chloride of zinc also acts in the same way as ammoniated oxide of copper, but it is a much less effective solvent. The dissolution takes place easier and quicker if the cellulose is first treated with concentrated cold sodium lye. Cellulose turns yellow to brown under the action of iodine. If saturated with a solution of iodine, it turns blue on concentrated sulphuric acid being added; and this forms a test of its presence. And if either wood or cellulose be boiled in dilute sulphuric acid, sugar is produced; but as yet it has not been found practicable to utilise this property commercially in making spirits from wood.

If the wood of broad-leaved trees be first purified with ammonia and then treated with alkali lye, xylan or wood-gum (C6H10O5) is produced, and when heated with dilute sulphuric acid this becomes xylose or wood-sugar (C5H10O5), a non-fermenting kind of sugar. The wood of coniferous trees, however, gives no xylan.

Concentrated acids are used for transforming cellulose for various industrial purposes. If unsized cellulose paper be plunged for 5 to 20 seconds into strong sulphuric acid and then thoroughly washed in water, the cellulose undergoes a colloidal modification and becomes amyloid or hydro-cellulose. It then resembles animal parchment, and becomes translucent, stiff, difficult to tear, and pliable in water without dissolving like common paper; and it is known by the trade-name of vegetable parchment.

If treated with concentrated nitric acid, or still better with a mixture of that and of concentrated sulphuric acid (which has a strong affinity for and absorbs water), the cellulose of purified cotton or of wood becomes transformed into a nitro-product, different combinations being formed according to the temperature and the length of time the acid is allowed to operate. Thus, taking the molecule of cellulose as having 12 atoms of C, the following combinations may be produced :

A mixture of 2 and 3 forms collodium-wool, which is soluble in æther-alcohol, and leaves a skin on evaporating, and which is used in photography and for surgical purposes. A mixture of the more strongly nitrated combinations 3, 4, and 5 forms gun-cotton, the explosive.

Nitro-cellulose is now also largely made into artificial silk in the St. Etienne district in France by Chardonnet's process. It is dissolved in æther-alcohol (2:3), and filtered under pressure. The filtered product (collodium) is then forced, under a pressure of about 50 atmospheres, or 700 lb. per square inch, through minute capillary glass-tubes so as to form extremely fine threads; and as this operation takes place under water, the solvent is absorbed by the water. Nine such threads spun together form a thread fit for weaving. The threads are denitrated with a solution of sulphate of lime, and are thus retransformed into almost pure cellulose. They have a silky gloss and dye well, but are far less than half as strong as natural silk.

Another product formed from gun-cotton is celluloid. After being slightly damped and ground down fine, gun-cotton is thoroughly mixed with an equal weight of camphor (pigments and other substances being also added), then subjected to strong hydraulic pressure at a temperature of 112° to 140° Fahr. The blocks thus formed are damped, softened by heating to 175°-190° Fahr., and then either rolled out into thin plates, or else pressed and dried in moulds, when they become a hard, homogeneous, translucent to transparent mass, from which combs, buttons, billiard-balls, cuffs and collars, imitation ivory and horn, &c., are made. Celluloid is highly inflammable, but this can be diminished by adding phosphate of ammonia or borated salts.

An amorphous form of cellulose is also sold under the trade name of viscose, which is of a gelatinous nature, and can be treated so as either to form threads fit for spinning, or transformed into a very hard substitute for celluloid (Schwackhöfer, op. cit., pp. 289, 323).

1. Wood-pulp consists of the disintegrated fibres of wood separated mechanically by grinding. It has much the same colour as the wood from which it is produced; and as it cannot be bleached, it is therefore desirable to use light-coloured wood for its production.

Spruce-wood is mostly used, then Silver Fir, but to a much less extent; and they both furnish a pale yellow pulp with fairly long fibre, which afterwards turns darker and duller in colour. Scots Pine is difficult to grind owing to its resinousness; but it gives a fine, though short, reddish-yellow fibre. Larch gives a coarse, short, reddish fibre. Among the broad-leaved trees, which all yield only a pulp of short fibre, Lime is the easiest to grind, and yields the largest out-turn; it gives a fine pale pulp, which afterwards darkens greatly and turns a dirty grey. Aspen and Poplar are also easy to grind, and give a very white pulp, which retains its light colour. Maple, Sycamore, and Hornbeam are difficult to grind, and give only a small out-turn of fine pulp of a pale colour.